The invention relates to an electrical grid simulation system and, more particularly, to an improved system and method for grid simulation that combines a reactive divider with a variable frequency converter to better mimic and control both expected and unexpected parameters in an electrical grid. The invention provides grid simulation in a manner that allows improved testing of variable power generators—such as wind turbines, solar inverters, energy storage devices, and power conditioning equipment (such as STATCOMS)—and their operation once interconnected within an electrical grid in multiple countries. Further, this invention enables improved testing of power generation devices for use in multiple countries with varying voltages, frequencies, and other operational characteristics.
Prior art grid simulation systems are unable to adequately test variable power generation equipment for use in standard applications that require interconnection to the electrical grid found in most countries. That problem is compounded when the power generation equipment is extremely large. Newer generation wind turbines are now manufactured on the multi-megawatt level and current test beds for such devices are limited in capability to adequately test such large devices.
The deficiencies in prior art systems are further compounded by the fact that electrical grids vary internationally. A robust fault ride-through testing system is not available that can emulate the multiplicity of electrical grids and their operational characteristics.
Prior art testing for compatibility and interoperability is often accomplished entirely with simulation or with hardware systems that offer limited fidelity in simulating real-world grid conditions or compatibility standards. Systems that can simulate steady-state conditions can often only do so at one frequency or at a limited range of grid variation and cannot replicate fault or widely dynamic conditions. Hardware devices for testing dynamic conditions, such as faults, are typically interconnected with a utility system and, therefore, limited in capability by that utility. It is also important to note that these systems subject the utility electrical grid to dynamic conditions that could be detrimental to its operation.
What is needed is a grid simulation system that will provide better control of a simulated grid to simulate faults and other parameters both expected and unexpected. An electrical fault on the level needed for testing ride-through capability of wind turbines, for example, is exceedingly difficult to create and control. It is therefore difficult with present systems to fully evaluate grid compatibility for multi-megawatt generators and similar devices such as power conditioning devices and loads.
Accordingly, an object of the present invention is to provide a grid simulation system that will provide the operator better control of the simulated grid, wherein the operator may more accurately, and with better control, simulate expected and unexpected parameters within the grid. Further, by using models of a real utility grid, the simulated grid could react and interact with the device(s) under test in a manner consistent with that expected in a real system. Such functionality might be achieved by using a real-time computer-based simulation that controls the hardware of the simulated grid and interfaces with it using appropriate sensor feedback.
Another object of the present invention is to provide a variable grid simulation system that will allow operators to evaluate grid compatibility for large generators in multiple other countries. More specifically, a robust fault ride-through (FRT) system with hardware-in-the-loop (HIL) capability is needed to properly emulate electrical grids found in multiple countries so that large generators may be fully tested for compatibility before installation into multiple types of electrical grids.
Another object of the invention is to provide an improved variable fault reactive device (VFRD) to allow for low-voltage ride-through (LVRT) and zero-voltage ride-through (ZVRT) testing of large generators to more accurately represent the testing and fault ride-through requirements of current and future grid codes.
Another object of the invention is to provide improved isolation transformers to provide more flexibility in fault testing for such systems.
Other objects and benefits of the present invention will become apparent from the detailed description when taken in conjunction with the drawings provided.